A frame structure of TDD (time division duplex) mode in an LTE (long term evolution) system is as shown in FIG. 1. In this frame structure, one radio frame of length 10 ms is divided into two half-frames, each half-frame is divided into 10 time slots with a length of 0.5 ms respectively, two time slots constitute one subframe with a length of 1 ms, one radio frame contains 10 subframes (numbered from 0 to 9), and one radio frame contains 20 time slots (numbered from 0 to 19). For a normal cyclic prefix (CP) with a length of 5.21 us and 4.69 us, one time slot contains 7 uplink/downlink symbols with a length of 66.7 us, wherein the length of the cyclic prefix of the first symbol is 5.21 us, and the length of the cyclic prefix of the other 6 symbols is 4.69 us respectively; for an extended cyclic prefix with a length of 16.67 us, one time slot contains 6 uplink/downlink symbols. Moreover, in this frame structure, the configuration characteristic of the subframe is that:
(1) subframe 0 and subframe 5 are fixedly used for downlink transmission;
(2) support uplink/downlink switch in the periods of 5 ms and 10 ms;
(3) subframe 1 and subframe 6 are special subframes that are used for transmitting 3 special time slots, i.e. a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS); wherein,
the DwPTS is used for downlink transmission;
the GP is guard time, without transmitting any data; and
the UpPTS is used for uplink transmission, and at least contains 2 uplink single carrier-frequency division multiple access (SC-FDMA) symbols used for transmitting a physical random access channel (PRACH);
(4) subframe 2 and subframe 7 are fixedly used for uplink transmission during uplink/downlink switch in the period of 5 ms;
(5) during uplink/downlink switch in the period of 10 ms, the DwPTS exists in two half-frames, the GP and the UpPTS exist in the first half-frame, the duration of the DwPTS in the second half-frame is 1 ms, the subframe 2 is used for uplink transmission, and the subframe 7 to subframe 9 are used for downlink transmission;
(6) primary synchronization (P-SCH) signals are transmitted on the first orthogonal frequency division multiplexing (OFDM) symbol in the DwPTS; secondary synchronization (S-SCH) signals are transmitted on the last OFDM symbol in time slot 1 and time slot 11, and the bandwidth in the frequency domain is 1.08 MHz; and
(7) at present, it is specified that the number of OFDM symbols contained in the DwPTS is at least 3.
A physical control format indicator channel (PCFICH) is transmitted on the first OFDM symbol in a common subframe.
A physical downlink control channel (PDCCH) is transmitted on the first n OFDM symbol(s) in the common subframe, and the n can be 1, 2, 3. Wherein, the value of the n is designated by the physical control format indicator channel.
Since the primary synchronization signals are transmitted on the first OFDM symbol in the DwPTS, in this way, for smaller bandwidths such as 1.25 MHz, the physical downlink control channel can not be transmitted on the first OFDM symbol in the DwPTS; therefore, the present invention provides a scheme to solve the problem of conflict between the primary synchronization signals and the physical downlink control channel in the DwPTS.